An integrated drive generator is used for generating three phase constant frequency alternating current in airframes. Integrated drive generators manufactured by the assignee of the present invention include a constant speed drive transmission having a differential. The differential functions to produce a constant speed output which drives a three phase alternating current generator from a variable input speed taken from a power takeoff from an airframe propulsion engine. The differential mechanically couples a first ring gear which is driven by a hydraulic pump and motor combination at a variable velocity to a second ring gear which drives the three phase alternating current generator at a constant velocity. A carrier supporting the differential is rotatably driven by the variable velocity input from the airframe propulsion engine.
FIG. 1 illustrates a simplified schematic of a prior art differential 10 manufactured by the assignee of the present invention which was used in an integrated drive generator. This schematic has been highly simplified in order to illustrate a lubrication system utilized in the prior art differential. The differential 10 includes a carrier 12 which rotatably supports a pair of planetary gears 14. The, carrier 12 is driven by a power takeoff from an airframe propulsion engine (not illustrated). The mechanical coupling of the carrier 12 to the airframe propulsion engine has not been illustrated which is connected to the right-hand portion of the carrier. A pair of bearings 16 rotatably support the carrier 12 in a housing (not illustrated) of the integrated drive generator (not illustrated). The carrier 12 has a pair of cylindrical openings 18 which are defined by cylindrical hollow shaft attached to the end plates 20 and 22 by a pin (not illustrated). Port 26, which extends between inner surface 28 and outer surface 30 of each hollow shaft 24, functions to transmit oil from the cylindrical opening 18 to journal 31 of planetary gear 14. The aforementioned pin insures that each hollow shaft 24 is disposed in a position which maintains the port 26 in a radial position located as far as possible from the axis of rotation of the carrier to insure high pressure oil being applied to the journals 31.
Lubrication of each of the journals 31 of the pair of planetary gears 14 is critical as a consequence of the high mechanical loads which they bear in transmitting torque between the variable speed output of a hydraulic pump and motor combination (not illustrated) which is applied to the ring gear (not illustrated) which drives the top planetary gear, torque applied from the variable speed power takeoff from the airframe propulsion engine which is applied to the right-hand portion of the carrier 12 and torque which is outputted to the output ring gear (not illustrated) driving a main generator (not illustrated) which is driven by the bottom planetary gear 14.
The lubrication system of the prior art differential of FIG. 1 is described as follows. Pressurized oil is provided from an oil source at a pressure such as 150 psi. The pressurized oil is applied to inlet 32. The oil flows from inlet 32 through openings 33 and axially along the cylindrical openings 18 between the ends 20 and 22. During operation, the carrier 12 is typically rotating at rotational velocities of several thousand revolutions per minute. The rotation of the carrier centrifugally accelerates the oil within the cylindrical openings 18 to cause it to flow radially outward toward the inner surface 28 of the hollow shaft 24. The clearance between the outer surface of the shaft 24 and the inner surface 31 of the gear 36 is typically several thousandths of an inch. Port 26 accepts oil at a pressure equal to the sum of the inlet pressure plus the centrifugal head and directs it to a groove (not illustrated) in the journal 31 to provide hydrodynamic bearing capability. The oil source supplies a flow rate of oil into inlet 32 which is greater than the combined flow rate through the port 26.
A splined coupling (not illustrated) couples the power takeoff from the airframe propulsion engine (not illustrated) to the carrier 12. This splined coupling requires lubrication to prevent fretting between the surfaces of the coupling. Oil is provided to the splined coupling by providing a port 35 to receive oil flowing outward from the axis of rotation. The position of the oil port 35 is not drawn to scale and is not intended to represent an actual position in the carrier side 22 of the assignee's integrated drive generators. The actual position of the opening 36 of the oil port 35 in different designs of integrated drive units of the assignee varied. However, it should be understood that the port(s) 35 in the prior art were not provided for receiving oil flowing outward toward each of the first ports 26 for deaerating the oil so that only deaerated oil moved radiallY outward to each of the ports 26 and for discharging a mixture of oil and air to the outlet 38.
The journals 31 of the planetary gears 14 are critical components which require high quality oil at all times during operation. The entraining of air within the oil being applied to the journals can shorten the life of the journals and lead to increased maintenance or premature failure.